In general, a driver of a vehicle may perform a downshift operation in front of a corner for the purpose of, for example, deceleration of the vehicle, stabilization of the vehicle behavior, or immediate generation of driving force at a rising of the corner. By performing the downshift operation in front of the corner, engine braking is effectively usable to achieve the deceleration of the vehicle, the stabilization of the vehicle behavior, or the like.
When the downshift operation is performed by a manual operation in an automatic transmission, the driver performs the downshift by selecting a speed change stage one by one through, for example, a shift lever operation in a manual range, or an operation on a paddle switch disposed on a steering wheel. However, multi-staging of recent automatic transmissions is remarkable, and it is therefore necessary to perform the downshift operation several times until obtaining an intended engine braking amount. This can be time consuming. For example, during traveling at a high speed stage, such as on high speed traveling, the high speed stage has a high ratio and there is a small ratio difference between a plurality of speed change stages. Hence, it particularly takes time to achieve the downshift from the high speed stage to an intended speed change stage.
For example, the following Patent document 1 discloses, as one of automatic downshift control, detecting a corner ahead of a vehicle and determining a speed change stage that becomes a target of downshift, taking the corner ahead into consideration. The following Patent document 2 discloses comparing, on the basis of a current position of a vehicle and road data, a current road shape and a shape on the road data, and restricting switching of speed change stages of an automatic transmission when there is a difference between the two, in cases where control of speed change stages of the automatic transmission is performed while traveling along a corner.
However, merely by performing the corner detection and downshift control according thereto as in the case with these conventional technologies, in some case, the downshift control according to characteristics of the corner is insufficient, or the result of the downshift control does not coincide with the driver's intention.
As an element that a driver considers while traveling along a corner, there is a distance to the vehicle ahead, besides the deceleration in front of the corner as described above. As a conventionally known control according to an inter-vehicle distance with the vehicle ahead, for example, Patent document 3 discloses acquiring information, such as a relative position and a relative distance with respect to the vehicle ahead, by a radar device, and controlling, on the basis of these information, a vehicle speed so as to carry out following travel to the vehicle ahead while keeping the inter-vehicle distance. For example, Patent document 4 discloses collision reduction brake control intended to avoid or reduce a collision by automatically activating a brake when an object ahead of a vehicle is detected by an external sensor, such as a camera and a radar device.